This invention relates generally to the art of forming one-piece, multiple groove pulleys from cup-shaped pulley blanks. There are significant problems in manufacturing concentric one-piece, single groove pulleys and those problems are compounded in the manufacture of multiple groove pulleys. For example, in a double groove pulley the grooves are separated by a land or circumferential rib located between the pulley grooves and which is an outwardly directed bulge between those grooves. During the formation of the pulley, that land must be supported by internal tooling within the cup, which serves as a backup as the pulley grooves are being formed. That tooling must be retracted from the land after the formation of the pulley grooves in order to permit removal of the completed pulley from the pulley-making machine. It has been proposed that such tooling be a removable rubber ring in the case of double groove pulley formed by segmented outer pulley groove-forming dies (U.S. Pat. No. 3,124,090) or such tooling may be segmented and expandable inner die employed in a spinning operation (U.S. Pat. No. 2,892,431).
It has been found that when using an internal segmented die to back the land, the segmented die tends to stick in the groove after the crushing operation, necessitating the hammering of the blank to free it from the die. A further disadvantage of segmented internal dies is the fact that many of those dies leave tooling marks on the pulley and provide a land which is not truly concentric.
Another type of internal tooling for forming the land between adjacent pulley grooves is a rubber block that will tend to expand into the land upon the application of axial pressure to the cup and which will return to a contracted position when the pressure is no longer applied. Although such rubber blocks do not tend to score the cup, they require frequent replacement and tend to change their dimensions upon repeated machine cyclings. An example of such tooling may be found in U.S. Pat. No. 3,124,090 and U.S. Pat. No. 2,929,345.